Modern automatic transmissions in automobiles may utilize an epicyclic/planetary gearbox to transfer power and function as a speed reduction unit. This epicyclic/planetary gearbox unit is composed of a sun gear driven by the input shaft of the transmission, multiple planetary gears that intermesh with the sun gear and are spatially arranged around the periphery of the sun gear, and an internal ring gear that intermeshes with and surrounds the multiple planet gears. The ring gear is generally the fixed member of the epicyclic/planetary transmission system. The multiple planetary gears are mounted to a carrier that in turn is operatively connected to the output shaft of the transmission. Vehicles possessing this configuration usually do not include an oil pump. When an oil pump is included, however, it is external to the epicyclic/planetary gearbox packaging.
Epicyclic/planetary gear reducers with the aforementioned packaging present several drawbacks. One drawback is that the gearbox or main rotor gear transmission is normally extremely heavy for a single subsystem. This is partially due to the oil pump being external to the epicyclic/planetary gearbox and therefore being less compact.
In addition, epicyclic gear reducers require lubrication to reduce friction and provide protection from wear for gear teeth, bearing surfaces, and other contact surfaces in relative motion. The planet gears submerge into a lubricant during revolution around the coaxial shaft of the transmission. Thanks to the revolution and the rotation of the planetary gears, the gears submerge into lubricant at a high tangential speed by some constructions. The wheel-body this hits the lubricant surface and accelerates the oil getting in its tooth valleys. Under this configuration, however, splashing may occur, which increases friction loss.
Thus, it is advantageous to provide a tighter packaging of the full assembly of an epicyclic/planetary gearbox with an internal integrated oil pump for transmissions, to reduce the weight of the unit, provide better lubrication, and avoid splashing.